1. Field of the Invention
The present invention relates to a fluorescent lamp with greater efficacy then previously available. The lamp has a non-circular cross-section through which the arc is spread by the inclusion of arc spreading initiators in the low pressure gas within the lamp. These arc spreading initiators cause the arc current to flow closer to the phosphored surface, thereby increasing light output.
2. Description of the Prior Art
The technique of magnetic arc spreading to increase efficacy and light output was described in co-pending applications Ser. Nos. 834,651 and 045,589, wherein magnetic fields spread the arc to occupy the full volume of the lamp. A similar effect, electric field arc spreading was utilized in a high intensity arc discharge lamp, co-pending application Ser. No. 117,950. These method of arc spreading utilize external forces created by magnetic or electric fields. The present invention accomplishes the same results with forces generated by the arc discharge through the rarified gas with arc spreading initiators, gaseous compounds, at low concentration within the lamp envelope.
When the arc current in a fluorescent arc discharge lamp lies closer to the phosphored wall, lamp efficacy is increased. One way of achieving this effect is with grooves or depressions placed in the long, essentially cylindrical envelope. Shurgan et al in U.S. Pat. No. 3,988,633 state that grooves alter the wall recombination rate of the plasma ions and increase the plasma arc stream length, thereby increasing luminous output.
When the arc is forced to move in response to an external force, the arc can be spread to fill the entire volume of a lamp envelope of any shape.
Gross and Skeist utilize magnetic arc spreading in co-pending applications Ser. Nos. 834,651 and 045,589 to spread the arc discharge throughout the lamp with a highly flattened elliptical or oval cross-section. Electrostatic forces can be applied to accomplish the same effect (U.S. patent application, Ser. No. 117,950). Campbell in U.S. Pat. No. 3,609,436 moves the discharge throughout an envelope by sequentially switching the arc to a multiplicity of electrodes.
Some fluorescent lamps are inherently unstable and the arc twists, swirls, or spirals within the long cylindrical envelope. The "Approved Method for the Electrical and Photometric Measurements of Fluorescent Lamps" (IES publication LM-9, par. 7-d, Sept. 1967) notes that "Swirling can usually be detected with the naked eye. However, there are also invisible or incipient swirls . . . These can usually be discovered by running a small permanent magnet along the length of the lamp. Any incipient swirling will evidence itself by a perceptible brightening at the spot where swirling exists." No application of this phenomenon to light production has been noted prior to this invention. Thus, an object of this invention is the provision of fluorescent lamps of greater efficacy and luminous output applying the phenomenon of arc spreading by initiators within gaseous contents of the lamp.
A further object of this invention is the availability of a multitude of lamp shapes possible since arc spreading frees the designer from the constraint of long, straight lamps of circular cross-section, 1.5" or less in diameter.
Yet another object of this invention is to provide a fluorescent lamp compatible with the Edison socket in order to realize the energy savings inherent in the greater efficacy of fluorescent lamps compared to the 17 lumens/watt output of a 100 watt incandescent lamp.